Wednesday, October 07, 2015

Branswell: H3N2 Remains the `Weak Link’ In The Flu Vaccine

Credit NIAID

#10,603

As I noted a couple of weeks ago in WHO: Recommended Composition Of 2016 Southern Hemisphere Flu Vaccine, six months after recommending an A/Switzerland/9715293/2013 (H3N2)-like virus for our seasonal flu vaccine, the WHO has already bumped that strain in favor of an A/Hong Kong/4801/2014 (H3N2)-like virus for use in next year’s southern hemisphere vaccine.

The field of H3N2 viruses is both complex, and rapidly changing. Far more so than H1N1, which remains antigenically similar to the virus that emerged in 2009.

During that same time period, seven distinct H3N2 genetic groups have been described (see ECDCInfluenza virus characterisation, Summary Europe, July 20151), making vaccine virus selection particularly challenging.Last year’s poor vaccine performance was due to the sudden rise in one of these antigenically different strains.

Today, I’m pleased to welcome back the inimitable Helen Branswell, who recently left the Canadian Press and now writes for the Boston Globe, who has fresh details on why this H3N2 subtype has been so difficult to match in the flu vaccine.

Culprit is ID’d as one targeting virulent strain

By Helen Branswell STAT October 07, 2015

This story was produced by Stat, a national publication from Boston Globe Media Partners that will launch online this fall with coverage of health, medicine, and life sciences. Learn more and sign up for Stat's morning newsletter at Statnews.com.

The reputation of the flu vaccine has taken a bit of a beating in recent years. Official claims about its effectiveness have been downgraded. And some years – like last year – the vaccine hasn’t been well-matched to the influenza viruses making people sick.

Now research points to a single component as the weak link in the vaccine, which is actually designed to protect against three or four types of influenza viruses.

Data being presented at a infectious diseases conference in San Diego this week show that the part of the vaccine targeting a strain known as influenza A H3N2 has cut the risk of infection by an average of only 38 percent in recent years.

The new research suggests the vaccine offers substantially stronger protection against the H1N1 subtype and influenza B – cutting the risk of infection by 60 percent to 75 percent.